Binder for foundry sand

ABSTRACT

A fluid, acid-hardening binder for foundry sand which is a resinous composition comprising 2.5-55 wt. % of composition (I), 30-95 wt. % of furfuryl alcohol and less than 40 wt. % of water, said composition (I) being obtained by reacting urea, glyoxal and formaldehyde under such conditions that the total number of moles of aldehyde groups, per mole of urea, is 2-4, the proportion of glyoxal aldehyde groups to the total aldehyde groups is 10-60%, the number of moles of glyoxal does not exceed the number of moles of urea and the number of moles of formaldehyde does not exceed 2.5 times the number of moles of urea.

United States Patent 1 Kawai et al.

[451 July 8,1975

[ BINDER FOR FOUNDRY SAND [75] Inventors: Hirotaka Kawai, Osaka; Hidetsugu Takenaka, Arita; Osamu Yamamoto, Wakayama, all of Japan [30] Foreign Application Priority Data Aug. 30, 1972 Japan 47-86848 [52] US. Cl. 260/29.4 R; 164/43; 260/39 SB; 260/DIG. 41; 260/69 R [51] Int. Cl C08g 51/24 [58] Field of Search 260/29.4 R, 39 SB, DIG. 40, 260/69 R; 164/43 [56] References Cited UNITED STATES PATENTS 2,876,062 3/1959 Torke et a1, 260/67.5

2,978,359 4/1961 Wedell 260/29.4 R 3,471,429 10/1969 Hayford 260/39 SB 3,709,849 1/1973 Lemon 260/29.3

Primary ExaminerL0renzo B. Hayes Attorney, Agent, or FirmWoodhams, Blanchard and Flynn [5 7] ABSTRACT A fluid, acid-hardening binder for foundry sand which is a resinous composition comprising 2.5-55 wt. of composition (1), 30-95 wt. of furfuryl alcohol and less than 40 wt. of water, said composition (I) being obtained by reacting urea, glyoxal and formaldehyde under such conditions that the total number of moles of aldehyde groups, per mole of urea, is 24, the proportion of glyoxal aldehyde groups to the total aldehyde groups is 10-60%, the number of moles of glyoxal does not exceed the number of moles of urea and the number of moles of formaldehyde does not exceed 2.5 times the number of moles of urea.

5 Claims, No Drawings ETNDER FOR FOUNDRY SAND BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acid-hardening binder for foundry sand comprising urea-glyoxalformaldehyde resin which emits little formaldehyde odor.

2. Description of the Prior Art Various binders for foundry sand have been proposed and many of them have been used with generally satisfactory results depending upon the size, scale of production, shape and material of the castings. Although urea-formaldehyde resins and ureaformaldehyde resin compositions containing furfuryl alcohol have been known as binders for foundry sand (for example, see Japanese Patent Publication No. 1543/T964), they have the disadvantage that they emit a strong formaldehyde odor. It is required to reduce this odor in order to improve working conditions in the foundry and to reduce air pollution.

SUMMARY OF THE INVENTION We have discovered that a resin composition comprising (A) a compound obtained by reacting urea, glyoxal and formaldehyde in critical proportions, mixed with (B) furfuryl alcohol and (C) water, is an excellent binder for foundry sand and that hardly any formaldehyde odor is emitted during the casting operation. The present invention has been attained on the basis of this discovery.

The reaction of urea, glyoxal and formaldehyde is known, and is disclosed, for example, in Japanese Patent Publication No. 545/1962. The products of this reaction are used generally for the treatment of fibers. The reaction mechanism and precise analysis of the reaction products have not been elucidated yet.

lt is surprising that, when a resin composition comprising urea-glyoxaLformaldehyde resin, furfuryl alcohol and water is used as binder for foundry sand, there is obtained the remarkable combination of properties that l little formaldehyde odor is emitted and (2) the binder possesses adequate strength. It is considered generally that in the condensation polymerization of urea-formaldehyde resin, methylene ether bonds are formed, a part of which is decomposed by heat to yield methylene bond thereby producing formaldehyde. On the other hand, in the system containing glyoxal, it is considered that the formation of methylene ether bonds is inhibited by steric hindrance or by other causes, or the bond formed is difficulty decomposed, or formaldehyde formed once by the decomposition is hardly expelled out of the system due to re-reaction. The mechanism is thus still unclear.

The composition of the binder of the present invention will be described below. Referring first to the urea-g1yoxal-formaldehyde composition, the critical proportions of the ingredients of this composition, according to the present invention, are defined by the following four items:

I. The total number of moles of aldehyde groups, per

mole of urea, is 24.

ll. The percentage of glyoxal aldehyde groups of the total aldehyde groups is 10-60%, preferably from l40%.

H1. The number of moles of glyoxal does not exceed the number of moles of urea.

Vll. The number of moles of formaldehyde does not exceed 2.5 times the number of moles of urea, preferably does not exceed 2.0 times the number of moles of urea.

Thus, the mol fractions of urea (U), glyoxal (G) and formaldehyde (F) have the following relations:

formaldehyde composition within the above general range are defined by the following formula (3), used in place of formula (3), and the following formula (5), used in place of formula (5):

0.1 2G/(2G F) 0.4

F/ U E 2 (5) with formulas (1), (2) and (4) remaining the same.

It has been confirmed, by experiments, that the above critical proportions must be employed in order to achieve the advantageous results that characterize this invention.

The order of mixing of the ingredients of the urea-glyo-xal-formaldehyde composition within the above composition limitations, is not critical. The composition is preferably reacted under substantially neutral conditions of pH 4.5-7.5, preferably pH 6.5-7.5, at a temperature of -l60C, preferably 80-120C for from about 30 minutes to 10 hours. The reaction should be continued until the amount of unreacted formaldehyde becomes to be less than 5 wt. preferably 3 wt. based on the amount of the entire reaction mixture.

The reaction may be effected in the presence of furfuryl alcohol and/or water in, a necessary quantity which will be shown below.

The acid-hardening binder composition for foundry sand according to this invention consists essentially of A. From 2.5 to 55 percent by weight, based on the total weight of the binder composition, of the urea-glyoxal-formaldehyde composition described above.

B. From 30 to percent by weight, based on the total weight of the binder composition, of furfuryl alcohol.

C. From 0 to 40 percent by weight, based on the total weight of the binder composition, of water.

If the binder contains less than 2.5 wt. of urea-glyoxal-formaldehyde composition the effect thereof as a binder is insufficient. Although furfuryl alcohol per se also reacts as a binder, the hardening velocity is insufficient. On the other hand, if the amount of the urea-glyoxal-formaldehyde composition is more than 55 wt. problems of fluidity, etc. occur during the operation. Water is not an essential ingredient of the binder composition but it may be present in an amount of up to 40 wt. for the purpose of regulating fluidity or the like.

3 In the above '.urea-glyoxal-formaldehyde composition, the the three ingredients should be reacted until the content of unreacted formaldehyde in the reaction mixture, which may contain furfuryl alcohol, is lowered to less than 5 wt. preferably lesszthan 3 The existence ornon-existence of furfuryl alcohol in the re- EXAMPLE 1 action mixture has no influence on the progress of the Mesh 20 35 -48 -65 reaction. That is to say, furfuryl alcohol can be added (-715) +20 +28 +35 +43 +65 to the urea-glyoxal-formaldehyde 1 reaction product 132 318 Wt. I 20.8 13.6 3.2

after the reaction has been completed or furfuryl alcohol can be added to ,a mixture of urea-glyoxalformaldehyde as a solvent and then the mixture can be I reacted. Thus,'furfuryl alcohol does not interfere with Chemical composition: v

the reaction of urea, glyoxal and formaldehyde. More than 99% sioz andsman quantities of A1203 In case urea, glyoxal and formaldehyde havebeen al- 1.3203, CaO and Mg ready reacted properly, furfuryl alcohol and water can be added-to the urea-glyoxaJ-formaldehyde composition bysimple blending. Since furfuryl alcohol has areactivity with hydroxyl groups in' the urea-glyoxal formaldehyde resin molecules, a polymerization (condensation) reaction may be caused to occur, butno such polymerization will occur at room temperature as far as a catalyst is not present. No polymerization of furfuryl alcohol will occur even at a temperature of about 100C and even if some of furfuryl alcohol would be reacted with the resin, it has no adverse effect on qualities of the. binder composition according to the present invention. v i t L I I In the preparation of a sand casting mold, a mixture of sand and anacid catalyst is blended withthe binder composition of the invention comprising said urea-glyoxal formaldehyde resin composition, furfuryl alcohol and water (optional) and molding is effected in the usual manner. The, preferred acid catalysts are phosphoric. acid and ptoluene-sulfohic' acid (PTS). Other acid catalysts for furan resins can also be used. The optimum amount of such acid catalyst depends on theiproperties of sand, the kinds of resin, etc., but it is usually in the range of l 0-1 00 wt. based ontheresin used. The amount of the'bindercornposition of'jthe i'nve ntio n employed is generally l-3 wt. based on the weight of sand. This can be changed suitably depending upon the properties of the sand mold required.

' Catalyst:

Method of evaluation: a 1 5 2 Kg of sand were blended together with 16g of the catalyst for 1 minute. The mixture was further blended together with 40 g of the binder for one minute.

mm/diameter X 50 mm test piece was molded. The test piece was stored in a constant temperature, constant humidity room. At 30 minutes and 24 hours after the molding, the compression strength (kg/cm) of the test piece was measured.

;Conditions of constant temperature room:

Temperature: 25C

Humidity:

= Preparation of binder'composition:

Predeterrnined amounts of urea and formaldehyde were dissolved under alkaline condition with heating. A predetermined amount of 40% glyoxal aqueous solution was added thereto at pH 7 and the whole was stirred at C for 2 hours.-The mixture was then stirred together witha predetermined amount of furfuryl alcohol at pH 6 at 90-100C for 3 hours to obtain binder composition. Binder compositions A through K were prepared in this fashion and test pieces were prepared therefrom as described above. The contents of unreacted formaldehyde .in the binder compositions were about 3% in No. D,. while about- .l2% in Nos. C,-

F, G, H and K.

.Composition of Binder Composition and Test Results Quantity (g) Compression Compression H O strength strength k No. I after 30 after 24 1 U 40%G PF FA Total minutes hours i (kg/cm) (kg/cm) A" 286 622 .34 .553 v 1495, m 25 0 13 B" 270 653 i 35 563 1521 26 0 ll C 363 177 405 1095- 22 1 23 D 141 254 208 354 957 19 l 36 15* 135 73 256 272 736 ll 4 42 F 55 243 272 735 10 5 24 G 193 52 227 277 749 9 5 25 H 207 49 219 279 754 8 5 38 I*" 300 290 106 409 1105 l7 0 41- J* 240 870 0 652 1762 30 0 7 K 195 109 212 303 819 12 5 49 (Note) U: urea, glyoxal, PF: parafqrmaldehyde, FA: furfuryl alcohol Y Th'e furfuryl alcohol iontent was adjusted to 37% in all cases but the water content jwas not adjusted.

- Although the amount of catalyst that provides optimum results in the respective binders may be different,

the tests were made employing the same amount of binder. *A, B. E, l and J are the compositions .noLwithin the scope of the invention. Compositions A, B and l are unsuitable because of their low initial strength. Composition .l is unsuitable because, ofv its poor final strength. Composition is also unsuitable. because it emits a strong formaldehyde odor, though it has sufficent strength,

EXAMPLE 2' U A commercially available binder Y (a resinous com- The invention is further described by reference to the following illustrative examples, which are not limiting.

position comprising urea-formaldehyde, furfuryl alcohol and water having a furfuryl alcohol content of 37% and a water content of 28%), was compared with a binder according to the invention (hereinafter referred to as KH O) having a furfuryl alcohol content of 37% 5 Compression strength Amount of formaldehyde (kg/cm evolved (ppm) After 30 after 24 Directly after after minutes hours blending minutes Y 2 37 195 199 K-H O 2 36 70 52 The results obtained by using 12 g of 70% paratoluene-sulfonic acid (PTS) in place of 16 g of 85% H PO were as follows:

Compression strength Amount of formaldehyde (kglcm evolved (ppm) After 30 after 24 Directly after after 10 minutes hours blending minutes Y 2 38 227 145 K-H O 2 43 21 26 EXAMPLE 3 516 Grams of a composition comprising 195 g of urea, 109 g of 40% aqueous glyoxal solution and 212 g of paraformaldehyde were reacted with furfuryl alcohol and water in the following quantities. Test pieces were prepared and the strengths thereof were measured in the same manner as in Example 1 and the following results were obtained. The catalyst used was 70% PTS (16 g).

Compression strength (kglcm No Amount of Amount of after After 24 hours FA (g) water (g) 30 minutes K 7748 112 2 40 K 9423 531 1 47 K, 3769 97* 6 66 1K 180 97* 3 11 K 152 93 l 3 K 418 461 l 22 K, 1396 880 l 35 The composition was dehydrated under vacuum to obtain anhydrous composition. K and K are not within the scope of this invention and they have only poor strength.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

11. A fluid, acid-hardening binder for foundry sand, consisting essentially of A. from 2.5 to 55 percent by weight, based on the total weight of the binder, of the reaction product of a urea-glyoxal-formaldehyde composition, in which 1. the total number of moles of aldehyde groups,

per one mole of urea, is from 2 to 4, 2. the percentage of glyoxal aldehyde groups of the total aldehyde groups is from 10 to 60%, 3. the number of moles of glyoxal does not exceed the number of moles of urea, and 4. the number of moles of formaldehyde does not exceed 2.5 times the number of moles of urea, said reaction product containing less than 5 wt. of unreacted formaldehyde, B. from 30 to 95 percent by weight, based on the total Weight of the binder, of furfuryl alcohol, and C. from 0 to 40 percent by weight, based on the total weight of the binder, of water.

2. A binder according to claim 11, in which the percentage of glyoxal aldehyde groups of the total aldehyde groups is from 10 to 40%, and the number of moles of formaldehyde does not exceed 2.0 times the number of moles of urea.

3. A binder according to claim 1, in which the reaction product is obtained by reacting urea, glyoxal and formaldehyde under conditions of a pH 4.5 to 7.5, and at atemperature of 80 to 160C until the content of unreacted formaldehyde in the reaction mixture is lowered to less than 5 wt.

4. A binder according to claim ll, in which the reaction product is obtained by reacting urea, glyoxal and formaldehyde under conditions of a pH of 6.5 to 7.5 and at a temperature of 80 to 120C until the content of unreacted formaldehyde is lowered to less than 3 wt 5. A composition for a sand mold, consisting essentially of sand blended with from about one to 3 percent by weight, based on the weight of sand, of a binder according to claim 1, and an amount of acid catalyst effective for hardening said binder. 

1. THE TOTAL NUMBER OF MOLES OF ALDEHYDE GROUPS, PER ONE MOLE OF UREA, IS FROM 2 TO 4,
 1. A FLUID, ACID-HARDENING BINDER FOR FOUNDRY SAND, CONSISTING ESSENTIALLY OF A. FROM 2.5 TO 55 PERCENT BY WEIGHT, BASED ON THE TOTAL WEIGHT OF THE BINDER, OF THE REACTION PRODUCT OF A UREAGLYOXAL-FORMALDEHYDE COMPOSITION, IN WHICH
 2. THE PERCENTAGE OF GLYOXAL ALDEHYDE GROUPS OF THE TOTAL ALDEHYDE GROUPS IS FROM 10 TO 60%,
 2. A binder according to claim 1, in which the percentage of glyoxal aldehyde groups of the total aldehyde groups is from 10 to 40%, and the number of moles of formaldehyde does not exceed 2.0 times the number of moles of urea.
 2. the percentage of glyoxal aldehyde groups of the total aldehyde groups is from 10 to 60%,
 3. A binder according to claim 1, in which the reaction product is obtained by reacting urea, glyoxal and formaldehyde under conditions of a pH 4.5 to 7.5, and at a temperature of 80* to 160*C until the content of unreacted formaldehyde in the reaction mixture is lowered to less than 5 wt. %.
 3. the number of moles of glyoxal does not exceed the number of moles of urea, and
 3. THE NUMBER OF MOLES OF GLYOXAL DOES NOT EXCEED THE NUMBER OF MOLES OF UREA, AND
 4. THE NUMBER OF MOLES OF FORMALDEHYDE DOES NOT EXCEED THE 2.5 TIMES THE NUMBER OF MOLES OF UREA, SAID REACTION PRODUCT CONTAINING LESS THAN 5 WT. % OF UNREACTED FORMALDEHYDE, B. FROM 30 TO 95 PERCENT BY WEIGHT, BASED ON THE TOTAL WEIGHT OF THE BINDER, OF FURFURYL ALCOHOL, AND C. FROM 0 TO 40 PERCENT BY WEIGHT, BASED ON THE TOTAL WEIGHT OF THE BINDER, OF WATER.
 4. the number of moles of formaldehyde does not exceed 2.5 times the number of moles of urea, said reaction product containing less than 5 wt. % of unreacted formaldehyde, B. from 30 to 95 percent by weight, based on the total weight of the binder, of furfuryl alcohol, and C. from 0 to 40 percent by weight, based on the total weight of the binder, of water.
 4. A binder according to claim 1, in which the reaction product is obtained by reacting urea, glyoxal and formaldehyde under conditions of a pH of 6.5 to 7.5 and at a temperature of 80* to 120*C until the content of unreacted formaldehyde is lowered to less than 3 wt %.
 5. A composition for a sand mold, consisting essentially of sand blended with from about one to 3 percent by weight, based on the weight of sand, of a binder according to claim 1, and an amount of acid catalyst effective for hardening said binder. 